That is, of course, a subjective determination. Does overseeing a major region for one of the world's largest pharmaceutical companies represent a step up from leading the company's biologics unit? Both are prominent positions and important jobs at AZ. One isn't subordinate to the other.

In any event, if the Latin American job was a promotion, it wasn't the kind of promotion Greenleaf was seeking. He left AstraZeneca last month and shortly lined up his next gig: CEO of Waltham, Mass.-based Histogenics Corp., a clinical-stage biotech focused on regenerative medicine.

"To be honest, I, as a leader, want to be with growth companies, smaller companies that are experiencing rapid growth, a little higher risk environments," Greenleaf told me in an interview Monday. "Looking at going to manage a region for a large pharmaceutical company really wasn't what I was looking to do with my career."

AstraZeneca sought to keep him with the organization, according to Greenleaf. Managing Latin America, he said, is "a coveted job, a good job. It's probably bigger than what I was looking to do."

At Histogenics, Greenleaf takes the helm of a company at an inflection point. The biotech, which last year closed a $49 million growth round led by Sofinnova Ventures, is pushing its lead product candidate — NeoCart, a knee cartilage implant grown from a patient's own cells — through late-stage trials.

Greenleaf said he believes Histogenics' work in soft tissue regeneration and cartilage repair is "second to none."

"Now we've got to prove that," he said. "We have to take it through our Phase 3 trial and get it regulatory approval and get it to patients. The data to date has been pretty extraordinary versus the current standard of care in this space."

Reflecting on the Maryland company he once led, Greenleaf said MedImmune is "probably in the best shape it's been in the seven years that I was there." AstraZeneca bought MedImmune in 2007 for $15.6 billion.